Correlation coefficients may be used for determining whether waveforms of signal or signals have similarity to each other. Heartbeat measuring devices adopt such a technology for calculating correlation coefficients. The heartbeat measuring device measures the interval of heartbeats of an operator based on electrocardiographic signals. The electrocardiographic signals are measured using a first electrode and a second electrode provided on a handle of a vehicle corresponding to the right and left hands of the operator thereon, and a reference electrode for measuring a reference potential.
In the above-described heartbeat measuring device, the grip pattern of the handle is determined using the correlation coefficient when correcting the time of the peak of the amplitude detected from the electrocardiographic signals. Specifically, the heartbeat measuring device calculates the correlation coefficient between a waveform of an electrocardiographic signal registered for each grip pattern and an electrocardiographic signal, thereby obtaining the similarity of the waveforms. Accordingly, the time of the peak of the amplitude is corrected based on the correction amount associated with the grip pattern of the waveform having the maximum similarity to the registered waveform of the electrocardiographic signal.
Patent Document 1
Japanese Laid-open Patent Publication No. 2012-239474
With the above-described technology, however, the waveforms in similar figures are determined as similar to each other, whereby the accuracy of determination on the similarity of the waveforms may be reduced.